Test kits are frequently used for the determination of the presence or concentration of an analyte in faecal samples. In general, there are therewith meant combinations of reagents and adjuvants necessary for the analysis. A test kit usually consists of several units but one-piece analysis elements are also available for faecal investigations which are also to be regarded as being test kits within the meaning of the present invention.
The investigation of faeces for the presence therein of occult blood is of particular practical importance. In the scope of the measures for the early recognition of carcinomas and pre-cancerousness of the colon and rectum, the detection of occult blood represents the recognised method.
In the case of such wide-scale investigations, a simple handling of the test kit is especially important. At present, there are usually employed the so-called test sachets which, encompassed by a covering of cardboard, have a sample layer which usually includes paper impregnated with guaiac. After application of the sample to a sample field on the surface of the sample layer, the sachet is closed on the front side.
The evaluation is usually carried out by the physician in that a flap on the rear side of the sachet is opened and on to the rear side of the guaiac-impregnated paper is applied a developer solution which contains hydrogen peroxide. In the case of the presence of blood in the faeces, a colour change is thereby obtained.
Having regard to the fact that the blood content of the faeces is frequently not homogeneous, in general, double sachets are used on which, in each case, two samples are simultaneously applied from different places of the faeces. Furthermore, it is usual to use in a test kit three such sachets with which, on three successive days, the faeces are investigated. Insofar as only one of these samples is positive, further investigations are indicated.
These test sachets for the investigation of faeces for occult blood substantially fulfil the requirements for the handling of such a test. The handling steps to be carried out not only by the patients but also by the physician are relatively simple and the test takes place sufficiently quickly. The evaluation can take place without the help of apparatus and the production of the test kits is comparatively economic.
However, this simple handling was hitherto only achieved in the case of faecal blood tests with the help of guaiac papers. However, this has considerable diagnostic disadvantages. In particular, on the one hand, it is not sufficiently specific and, on the other hand, in many cases it is not sufficiently sensitive.
The deficient specificity is to be attributed to the fact that the detection method based on the pseudoperoxidase reaction of the haemoglobin also reacts on other components of the faeces, for example with animal blood introduced with the nutriments. In order to avoid falsely positive findings, the test must, therefore, be carried out with the use of a controlled diet.
Furthermore, there is knowingly used a relatively high sensitivity threshold. This in turn has the disadvantage that the danger exists that small blood concentrations, which are, nevertheless, clinically relevant, are overlooked so that falsely negative findings are obtained.
Because of these disadvantages, numerous attempts have already been made to use other test principles for the analysis of faecal components and especially for the detection of occult blood. Recently, immunological processes have, in particular, been suggested in which there are used binding components (Hb-antibodies) which are immunologically specific. However, such test kits are laborious to use.
In particular, the known immunological investigations of the faeces usually require laborious sample preparation measures. The sample must usually be homogenised, thereafter mixed with a liquid and finally centrifuged. Only the so produced pure supernatant can be used as sample liquid.
Under the trade name "Hemolex", there is known a test kit made by Orion, Finnland, for the immunological determination of haemoglobin in faeces which avoids centrifuging. Nevertheless, the procedure is very laborious. For example, the faeces must be homogenised immediately in a fresh state and taken up in a special solution. Insofar as this is not possible, the sample must be stored in a freezer.
From Federal Republic of Germany Patent Application No. 34 02 938, there is known a diagnostic aid for the immunological determination of haemoglobin in faeces in which a solid, rod-shaped carrier, which is coated with the antibody, is dipped directly into the faeces. The further evaluation requires several wet chemical steps, especially washings, and is, therefore, laborious.
From European Patent Specification No. 0,032,742, a test kit is known in which a formed body, preferably produced from synthetic resin, is used in the sample application region of which is present a filter paper impregnated with guaiac. However, this here not only serves for the detection but, at the same time, for filtering the sample. Whereas this is applied to the front side of the paper, on the rear side there is present an untreated filter paper. Due to the special construction of the formed body, it is possible to press together the sample, whereby the haemoglobin passes from the sample, together with liquid sample components, through the guaiac paper into the untreated filter paper. For the evaluation, the filter paper is removed and evaluated wet chemically.
It is an object of the present invention to provide a test kit and a process for the evaluation of faeces in which laborious handling steps, especially a preparation of the sample, are avoided.